The present invention relates to a vibration apparatus for producing minute vibrations. More particularly, the present invention relates to a vibration apparatus for producing minute vibrations for use in testing the effect of such vibrations on precision measuring devices.
In general, the floor of a room on which a measuring device is disposed is always subjected to extraneous minute vibrations. The frequency of such vibrations is, in general, within a range from 1 to 50 Hz and the amplitude thereof is very small, being less than about 10.mu.m. Even so, such vibration of the floor causes measuring devices disposed thereon to vibrate also. Therefore, when the measured value is to be highly amplified, it becomes difficult to obtain a precise measurement because extraneous floor vibrations influence the measured value. Accordingly, when the measured value is to be highly amplified, it is desirable to know the extent to which extraneous floor vibrations affect the reading of the measuring device.
To determine the influence of floor vibrations on the reading of the measuring device, it is sufficient to know the relationship between the floor vibrations and the reading of the measuring device. However, the frequency spectrum of floor vibrations is generally within the range from 1 to 50 Hz. The vibrations, however, are not generally spread uniformly over this frequency band but are often concentrated within a very narrow range. Therefore, the above mentioned relationship cannot easily be determined for frequencies outside this narrow range. In order to overcome this problem, a vibration test using a vibration apparatus becomes necessary. However, conventional vibration apparatuses are designed for use in testing equipment for resistance to vibration and are therefore capable of producing large-amplitude or high-acceleration vibrations. Thus when such an apparatus is used to produce a very small vibration (minute vibration), it is very difficult to produce a vibration having a desired waveform because of the influence of the minute vibrations of the floor upon which the apparatus stands. To overcome this problem, the vibration test may be performed at a large amplitude and large acceleration. In this case, however, although the vibration of the floor will become relatively neglegible, the measuring device itself will be put under much different conditions from the normal desired conditions. This leads to two obvious disadvantages. First, it is difficult to theoretically determine the effect of the vibrations to which the apparatus is subject in normal use from the effect of the vibrations used in the test because of the non-linearity of the parameters in such test employing large amplitude and large acceleration. Second, there is a possibility of damage to the apparatus itself. Therefore, in order to measure the effect of vibrations on the reading of the measuring device, it is preferrable to test the device using minute vibrations similar to floor vibration. For this reason, there is required a vibration apparatus which can provide minute vibrations simulating floor vibration without itself being influenced by extraneous floor vibrations.
Accordingly, the object of the present invention is to provide a vibration apparatus which can readily produce minute vibrations in simulation of any type of floor vibration.